1. Field of the Invention
The present invention relates to generally and, more particularly, but not by way of limitation, to a novel method of battery charge restoration based on estimated battery plate deterioration and/or based on battery state of health.
2. Background Art
When used herein in connection with a battery, the term xe2x80x9cplatexe2x80x9d refers to a battery electrode, regardless of configuration.
While the present invention has been described principally with respect to a float charging system, it will be understood that the invention may be applied as well to any situation in which a battery or batteries can be suitably modeled in accordance with the principles of the invention.
As used typically in telecommunications power supply systems which require a precise and uninterrupted supply of electrical power, a bulk charger is connected to furnish a predetermined voltage across a voltage-controlled load. To ensure uninterrupted power, one or more strings of batteries are also connected across the load to supply power in the event of an outage of the bulk charger, the string or strings of batteries in this configuration comprising part of a xe2x80x9cfloat charging systemxe2x80x9d.
In the past, when flooded batteries were employed in air conditioned environments, such systems were very reliable and produced a very precise voltage. Today, many such installations, particularly the smaller ones which have recently proliferated, have replaced the flooded batteries with valve-regulated, lead-acid (xe2x80x9csealedxe2x80x9d) (VRLA) batteries. The principal reason for the change is elimination of maintenance. Also, again particularly in smaller installations, it is desirable for packaging reasons to lay the batteries on their sides. An ancillary benefit of this arrangement is that the batteries have a longer life when placed on their sides because of the lower specific gravity gradient across the batteries.
In such installations, the typical method of charging the batteries is to bulk charge all the batteries continuously at a float voltage. If necessary, the bus voltage can be raised. The latter is undesirable for a number of reasons, not the least of which is that the elevated bus voltage tends to stress the electrical and electronic components of the system and particularly the contactors in the load system. Alternatively, one or more of the batteries could be taken out of service and charged, but this requires additional maintenance effort. Another alternative is to try to balance the voltage to minimize both positive plate corrosion and negative plate self-discharge. However, one is faced with the problem of holding the bus voltage a bit high and causing corrosion of the positive plate of the battery or holding the bus voltage a bit low and causing self-discharge of the negative plate of the battery. If the self-discharge is serious enough, battery capacity can drop, and the negative plate can ultimately experience severe and irreversible sulphation. Fortunately, neither the corrosion nor the self-discharge process is terribly injurious if it occurs for only a small percentage of the running time of a battery.
Some attempts to prevent self discharge or to reduce the difference between the positive and negative plates have included the use of catalysts and the use of special alloys.
Accordingly, it is a principal object of the present invention to provide a method of charge restoration based on calculation of the degradation of a battery operating with a predetermined terminal voltage that does not require taking batteries off-line nor, preferably, raising the bus voltage.
It is a further object of the invention to provide such a system that operates at a voltage designed to xe2x80x9cbalancexe2x80x9d positive plate corrosion and negative plate self-discharge.
It is an additional object of the invention to provide such a system in which the calculation of degradation of the battery includes such factors as temperature of operation, length of time of operation of the battery, battery calendar age, and/or type of discharges to which the battery is subjected.
It is another object of the invention to provide a system in which measurement of terminal voltage after a charge restoration can be used to indicate the state of health of the battery.
A further object of the invention is to provide such a system that operates at a relatively low duty cycle such that it is available to service a number of strings of batteries.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.
The present invention achieves the above objects, among others, by providing, in one preferred embodiment of the invention, a method of restoring charge to a battery operating with a predetermined terminal voltage, comprising: determining an expected rate of degradation of a plate or plates of a battery in terms of decrease of capacity per unit time and temperature of operation of said battery to determine a degree of degradation of capacity of said battery; and providing sufficient charge to said battery to restore a predetermined degree of said capacity of said battery. In another preferred embodiment of the invention, a method of diagnosing state of health of a battery, comprising: restoring a theoretical amount of charge to a partially depleted battery; and examining how said battery responded to said restoring a theoretical amount of charge to said partially depleted battery to determine said state of health of said battery.